Saikin Kono Sekai wa Watashi Dake no Mono ni Narimashita...... - Vol. 2 Ch. 31 - That Guy Again.

[MangaDex]

 

[TaintedAardvark]

I think this story's about her coming to terms with her life. Different characters represent different parts of herself or her past she's facing.
Mutsuki is her innocent self, about to be killed by the stalker, who is the man she planned to give her virginity to (and was raped by).
The child/boy is her brother? And the big guy was...I don't know, I didn't think this through, but I'm onto something.